This invention relates to a fire resistant asphalt composition and, in particular, to an asphalt composition which is incorporated into a fire resistant roofing system.
The prior art is replete with fire resistant roofing systems which incorporate bituminous asphalt compositions. Some of these roofing systems may utilize one or more layers of fiberglass, polyester or other mats into which may be incorporated an asphalt composition. This type of construction is disclosed in U.S. Pat. Nos. 4,420,524 and 4,638,228 to Gorgati in which a three layer roofing membrane comprises an upper fiberglass mat, a fiberglass net and a polyester mat layer, each layer being impregnated with a bitumen mixture which includes a thermoplastic polymer. Other patents have disclosed various fire-retardant asphalt compositions for use in roofing applications such as U.S. Pat. No. 4,804,696 to Jolitz et al and U.S. Pat. No. 4,659,381 to Walters, the latter incorporating a halogenated flame retardant such as decabromodiphenyl oxide, an inorganic phosphorus compound, and a metal oxide hydrate such as zinc borate hydrate.
Ideally, asphalt based roofing systems will have membranes of one or more layers into which is added a waterproofing, fire resistant composition such as a bitumen based asphalt. The amount of any additives providing the fire resisting characteristics should be minimized to reduce costs while still permitting the roofing system to meet Underwriters Laboratories standard UL 790, class A. In addition to being fire resistant, the membrane system should have high strength and stability for long life, and should be easily manufactured at reasonable cost. While prior aft roofing systems halve attempted to meet these criteria, commercially available roofing systems have been inadequate in one or more areas.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a waterproofing membrane system for roofing and other building applications which has good fire resistant characteristics.
It is another object of the present invention to provide a fire resistant bitumen based asphalt composition for incorporation into the membranes of a roofing system.
It is a further object of the present invention to provide a fire resistant asphalt composition in which the fire resisting additives make up a relatively low percentage of the asphalt.
It is yet another object of the present invention to provide a fire resistant roofing system which minimizes the number of substrates or membranes necessary to result in good performance.
It is a further object of the present invention to provide a fire resistant roofing membrane system which meets the above objects and which is easy to manufacture and reasonable in cost.